The invention relates to an exhaust gas turbocharger for an internal combustion engine having a fresh gas supply device. The invention also relates to a corresponding arrangement for supplying fresh gas to an internal combustion engine.
Internal combustion engines, e.g. diesel engines, are often fitted with exhaust gas turbochargers. FIG. 1 shows a prior-art internal combustion engine 1, the exhaust gas line 6 of which is connected to an exhaust gas turbine 12 of an exhaust gas turbocharger 10. This exhaust gas turbine 12 drives a compressor 11 of the exhaust gas turbocharger 10, with the exhaust gas turbine 12 and the compressor 11 here being coupled by a turbocharger shaft 13. The compressor 11 compresses intake air from a fresh gas inlet 2 and thus increases an intake pressure in an intake line 5 of the internal combustion engine 1. An acceleration behavior, for example, of a vehicle (not shown) fitted with the internal combustion engine 1 is thereby improved. Moreover, a reduction in fuel consumption is achieved.
Compressor rotors of exhaust gas turbochargers in internal combustion engines are produced from aluminum or aluminum alloys or from titanium or titanium alloys. The reason for this is their low density and hence their low mass moment of inertia. This favors rapid acceleration of the turbocharger and hence reduces “turbo lag”. This turbo lag arises in internal combustion engines with exhaust gas turbochargers because, during an acceleration process, the exhaust gas mass flow from the internal combustion engine 1 through the exhaust gas turbine 12 must accelerate the compressor 11 of the exhaust gas turbocharger 10 to enable it to build up its full boost pressure. The time before the maximum boost pressure is reached depends decisively on the inertia of the rotors (of the exhaust gas turbine 12 and of the compressor 11). The lower the mass moment of inertia, the greater is the reduction in the turbocharger speed during a shift operation or gear change (especially in the case of manual transmissions and automated shift transmissions). The result is that, after clutch engagement, the exhaust gas turbocharger 10 must first of all be reaccelerated to the required speed, which corresponds to the engine speed at that time.
Solutions have been proposed to enable this turbo lag to be overcome, wherein compressed air sourced, for example, from a compressed air reservoir 8 fed by an air compressor 9 is introduced in a controlled manner into the intake line 5 of the internal combustion engine 1 in order to cover an increased intake air requirement of the internal combustion engine 1 when this occurs. This is accomplished by use of a fresh gas (unburnt gas) supply device 4, which is arranged between the compressor 11 of the turbocharger 10, or a charge air cooler 3 fitted downstream in the direction of flow, and the intake line 5.
WO 2006/089779 A1 describes a device for supplying fresh air to a turbocharged piston-type internal combustion engine and a method for operating the same.
It is therefore the object of the present invention to provide an improved exhaust gas turbocharger.
This and other objects are achieved by an exhaust gas turbocharger having for an internal combustion engine, in particular a diesel engine, having a fresh gas supply device. The exhaust gas turbocharger comprises wherein the exhaust gas turbocharger comprises at least one compressor; at least one exhaust gas turbine; a turbocharger shaft, by which the at least one compressor and the at least one exhaust gas turbine are coupled for conjoint rotation; and an energy storage device for increasing a mass moment of inertia, wherein the energy storage device is coupled to the at least one compressor and the at least one exhaust gas turbine for conjoint rotation by way of the turbocharger shaft.
One aspect of the invention consists in fitting the exhaust gas turbocharger with an energy storage device, which increases a mass moment of inertia of the exhaust gas turbocharger.
In contrast to the fact that an increase in the inertia of the exhaust gas turbocharger, i.e. of the rotating components, leads to a significant increase in “turbo lag”, a combination in an arrangement of an exhaust gas turbocharger and a fresh gas supply device has the advantage that the exhaust gas turbocharger is synchronized with the existing engine speed after a gear change to such an extent that there is no need to accelerate the exhaust gas turbocharger to a turbocharger speed required for the existing engine speed in order to obtain an associated boost pressure.
Another advantage is that the compressed air consumption of the fresh gas supply device is reduced since acceleration of the exhaust gas turbocharger after a gear change is eliminated.
For this purpose, the energy storage device has a rotating mass. It can be designed as a kind of flywheel mounted on the turbocharger shaft for conjoint rotation. This rotating mass can also be at least partially integrated into the turbocharger shaft, thereby reducing the number of parts.
The rotating mass of the energy storage device may be distributed in such a way that it is integrated at least partially into rotating parts of the at least one compressor and/or of the at least one exhaust gas turbine. This is possible, for example, if the rotors of the compressor and/or the exhaust gas turbine are produced from steel.
In a preferred embodiment, the rotating mass of the energy storage device can be specified for a predetermined retardation of the speed of the exhaust gas turbocharger, thereby reducing the compressed air consumption of the fresh gas supply device. At the same time, the efficiency of the internal combustion engine is increased.
Moreover, a reduction in compressed air consumption avoids adaptation of an air compressor of the compressed air system for the additional air or of an air drying system since, by virtue of the energy storage device, there is no extra increase in the requirement for additional air that would necessitate adaptation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.